We’ve all experienced it: the stomach-turning whiff of rotting rubbish as we wheel the bin out, drive past a landfill, or catch a factory’s sour pong. But imagine living with that stench day in, day out.
Surprisingly, we rarely stop to think about how such odour pollution affects our health or quality of life. Bad smells are often brushed aside as trivial or just a matter of taste. Studies show people generally rank their sense of smell as less important than sight, hearing, touch and taste. Some US university students even said they’d rather lose their sense of smell than give up their mobile phone.
Yet the discomfort is only part of the story. Research has linked unpleasant urban odours to a range of health complaints, including headaches, nausea, breathing problems and disrupted sleep. There can also be longer-term mental and physical effects. A growing field of science is now revealing just how deeply scent influences our bodily and mental wellbeing, reports BBC.
Why bad smells trigger alarm
Our sense of smell evolved partly as an early warning system to keep us away from infection. Something that smells off is often full of harmful bacteria.
Johan Lundström at Karolinska Institute in Stockholm, Sweden describes this as part of our “behavioural immune system”. “The olfactory system’s main job is to help us avoid danger in the environment,” he says. His research shows that within roughly 300 milliseconds of inhaling a bad odour, the brain processes it and the body instinctively recoils.
This defensive wiring means we can easily be convinced that an unknown smell is bad, even if it’s normally pleasant. Lundström notes, “If we detect an odour we don’t recognise, it’s almost always a negative experience.”
When a smell becomes linked to a threat, our sensitivity to it can skyrocket. In one experiment, Lundström’s team found that pairing a scent with a mild electric shock made people detect that same smell at far lower concentrations – an evolutionary trick to help us react swiftly to danger.
Similarly, hydrogen sulphide (the classic rotten eggs gas from sewage) can be smelled at just 0.5 parts per billion, acting as an early alarm for a gas that turns lethal at higher levels.
Real physical and mental effects
It’s not all about threat, though. Pleasant smells – like a forest’s fresh fragrance – can boost mental health by activating brain regions tied to emotion and memory.
But the reverse is also true. A 2021 review of studies found “biological plausibility” linking bad smells to symptoms like headaches or vomiting. For example, foul odours can stimulate the vagus nerve, which connects the brain and gut, causing nausea. However, the same review concluded that more research is needed to draw firm conclusions.
How much a bad smell affects you also depends on how anxious it makes you feel. Pamela Dalton, a cognitive psychologist at the Monell Chemical Senses Center in Philadelphia, US has spent 32 years studying this.
“The health impact comes through an individual’s dislike or fear of an odour,” she explains. The more worried you are, the worse the effect on your health and wellbeing.
When a stench changes your life
A persistent bad smell can quietly reshape daily life. People may start making “maladaptive” changes – keeping windows shut on hot days, avoiding outdoor exercise, or staying away from social gatherings.
Still, reactions vary wildly. Some people find the faintest whiff unbearable; others barely notice it. Age, gender, allergies and smoking all play a role, says Dalton, who frequently investigates odour complaints.
You don’t really get used to it
You might assume people simply get accustomed to a bad smell over time. But repeated exposure to unpleasant odours – from landfills, for instance – doesn’t actually make them easier to tolerate.
By contrast, we do habituate to neutral or pleasant smells. Lundström explains, “Once you’ve smelled something and realised it won’t kill you, you stop being able to smell it.” That’s why, even though the human nose can detect a trillion different odours, most of us struggle to name harmless everyday smells like coffee or vanilla. Less than half of people can correctly identify them in sniff tests.
Not all communities suffer equally
A stench can be strangely local – sometimes only appearing when the wind changes, or only on one street. Amanda Giang, associate professor at the University of British Columbia, calls it “hyperlocal”. “I could live a block away and never know the next block smells of rotting fish.”
But some neighbourhoods bear the brunt. Cheaper housing often sits closer to smelly landfill sites or heavy industry. Studies in Europe and the UK have found that low-income communities are more likely to live within a 1.25-mile (2km) radius of waste incinerators, landfills and hazardous waste sites than wealthier areas.
The good news: complaints can force change. Sewage plants and fish processing factories have been scaled back or shut down after residents campaigned. Around the world, efforts to control odour pollution are growing – from new Chilean rules on fish-feed plant smells to tighter Lithuanian limits on how much stink companies can release near homes.
An unexpected upside
Living with constant bad smells is hard. But there is one small silver lining: a working sense of smell is a sign of good health.
Around 5 percent of people have no sense of smell at all – a condition called anosmia. They often suffer significant health consequences. Interviews with anosmia sufferers reveal they struggle with poor appetite and lower-quality diets because eating becomes joyless. Lundström says, “If you lose your sense of smell, your appetite goes away.”
Even more striking: research shows that older adults with a poor sense of smell have a 46 percent higher risk of dying within ten years. Scientists are still unpicking the reasons, but they suspect links to cardiovascular disease and neurodegenerative conditions like Alzheimer’s and Parkinson’s.
